drm/msm/mdp4: get rid of struct mdp4_platform_config

Struct mdp4_platform_config is a relict from the DT-conversion time.
Move the max_clk field to the mdp4_kms_init(), the place where it is
used and drop the struct mdp4_platform_config and the mdp4_get_config()
function.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/485050/
Link: https://lore.kernel.org/r/20220505135008.1351533-3-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>